Reseach On Magneto-optic Dynamics Properties And Strain Manipulation Mechanism In Endohedral Fullerenes

In recent years,magnetic endohedral fullerenes have been a hotspot in international scientific researches.Because of their unique hollow cage structures,which can be encapsulated into different atoms,molecules,or clusters,endohedral fullerenes have become a unique new type of functional nanomaterials,and have great potential applications in the fields of mechanics,physics,chemistry,biomedicine and energy source.In this thesis,three typical magnetic endohedral fullerenes Ni@B₈₀,Y₂C₂@C₈₂ and Sc₃N@C₈₀ are selected as the main research objects,and their structural stability is calculated and analyzed based on the?-process theoretical model and first-principles method.What's more,different strains have been applied to the systems in order to study the strain modulation mechanism on the ultrafast magneto-optic dynamics of three kinds of magnetic endohedral fullerenes from the mechanical point of view.This paper includes the following four aspects:(1)For the initial structures of three magnetic endohedral fullerenes Ni@B₈₀,Y₂C₂@C₈₂ and Sc₃N@C₈₀,Hartree-Fock method is used to optimize the structures and analyze the natural frequencies.The corresponding stable structures are obtained on the premise of energy minimization and no imaginary frequencies.Then the ground and excited states properties of three kinds of magnetic endohedral fullerenes are calculated and analyzed by the symmetry adapted cluster-configuration interaction method(SAC-CI).(2)For the endohedral fullerene Ni@B₈₀ molecule,on the basis of achieving ultrafast spin-switching process in the system,strains are applied step by step along different directions of the Ni@B₈₀ molecule,and the secondary optimization is made.Compared with the structure of the non-strained Ni@B₈₀ molecule,the Ni@B₈₀molecule has no obvious change,and its original symmetry is still maintained.At the same time,the spin density of the molecule system is still highly localized on the Ni atom under the strain effect,and the spin density distribution keeps around 1.Based on the?-process theory,the spin-switching processes in Ni@B₈₀ molecule have been achieved.When 1.0%strain is applied along the number 68 and 78 boron atoms line direction,it takes about 400 fs;when 1.0%strain is applied along the vertical two parallel and opposite boron pentagons,it takes about 1300 fs.(3)For the double-magnetic-center endohedral fullerene Y₂C₂@C₈₂-C₂(1),the results show that the geometry of the optimized enclosed Y₂C₂ cluster is basically consistent with the theoretical results of predecessors through structural optimization calculation,and is also very close to the experimental data.In addition,in the Y₂C₂@C₈₂-C₂(1)system,it is found that the spin density is highly localized on the two Y atoms and only minimally distributed on the carbon cage.The spin-switching and spin-transfer processes are achieved in the same endohedral fullerene system under the?-process.The achieved spin-switching scenario completes within about1000 fs and its fidelity reaches 97.8%,while the obtained spin-transfer process completes within 200 fs and its fidelity reaches 95.1%.(4)In view of the synthesized metal nitride cluster fullerenes Sc₃N@C₈₀,the effect of strain on the magneto-optic dynamics of the molecule system has been explored.For the initial structure of Sc₃N@C₈₀,the calculation results show that the spin density of the system is highly localized on three Sc atoms,and the spin-switching process is achieved based on the?-process theory,but the spin-transfer process can not be achieved.When different initial intermediate states are selected in the spin-switching processes,the processes have obvious differences,among which the shortest time is 400 fs and the longest time is 1000 fs.However,It is worth noting that in the Sc₃N@C₈₀ system,spin-switching and spin-transfer processes can be achieved at the same time in sub-picosecond scale when a suitable strain is applied to the molecule system.In addition,when the same laser pulse is adopted,the reversible spin-transfer process also has been achieved and shows perfect time inversion properties compared with the spin-transfer process.